This invention relates to the coil springs of a brush device, and more particularly to an improvement of brush pushing compression coil springs used for electric rotary machines.
FIGS. 6 and 7 are a front view and a side view, respectively, showing a compression coil spring employed in a conventional brush device of a starter motor. FIGS. 8 and 9 are sectional views showing a brush accommodating member in which a brush is set being pushed by a compression coil spring. In those figures, reference numeral 1 designates an elliptic compression coil spring made of a steel wire. Both end portions of the spring 1 are closely coiled as indicated at 1a when compared with the remaining middle portion. The outer end part of one of the two closely coiled end portions 1a is coiled elliptic as indicated at 1b (hereinafter referred to as "a coiling start end part 1b", when applicable), and similarly the outer end part of the other is coiled elliptic as indicated at 1c (hereinafter referred to as "a coiling finish end part 1c", when applicable).
Further in FIGS. 6 through 9, reference numeral 2 designates a brush pushed by the compression coil spring 1. The brush, as shown in FIG. 9, has a rectangular abutting surface 2a against which the compression coil spring 1 is abutted. Reference numeral 3 designates the lead wire of the brush 2; and 4, a brush holding frame having an accommodating section 4a, in which the compression coil spring 1 and the brush 2 are held.
Reference numeral 5 designates an insulating board covering the opening of the accommodating section 4a of the brush holding frame 4. The insulating board 5 is formed by molding synthetic resin.
The conventional brush device constructed as described above, is assembled as follows: First, the brush 2 and the compression coil spring 1 are set in the accommodating section 4a of the brush holding frame 4, and then the opening of the accommodating section 4a is covered with the insulating board 5.
The above-described conventional brush device has following problems: If the brush device is limited in diametrical dimension, the brush length is maintained unchanged, then the compression length of the compression coil spring is limited. Hence, in this case, it is difficult to sufficiently provide closely coil both end portions of the compression coil spring 1, as a result of which the brush 2 and the elliptic compression coil spring 1 are not snugly abutted against each other, and therefore sometimes the brush 2 may be cracked. On the other hand, sometimes the end of the compression coil spring 1 may stick out over the abutting surface 2a of the brush 2 because of the variations in dimension of the elliptic compression coil spring 1 when manufactured. Moreover, when a number of elliptic compression coils springs are conveyed before assembling, they may be tangled with one another like puzzle rings. If once the elliptic compression coil springs are tangled, then it is rather difficult to untangle them.
Accordingly, an object of this invention is to eliminate the above-described difficulties accompanying a conventional brush device. More specifically, an object of the invention is to provide a brush device which is free from difficulties that the brush is cracked, and the end of the compression coil spring sticks out over the abutting surface of the brush, and the elliptic compression coil springs are entangled with one another during conveyance.